Combinatorial Approach to Boson Anti-Normal Ordering Problem

We address a systematic combinatorial approach to the anti-normal ordering problem. In this way, we use the Stirling numbers and their generating function, the so-called Bell polynomials, together with the operational methods to anti-normal the operator ${e^{\lambda {a^\dag}a}}$. In fact, we exploit the new theorem given by Sh\"ahandeh et al. in a special case of anti-normal ordering.